The present embodiments relate to a method and apparatus for transmitting a counter signal in an imaging system.
Magnetic resonance devices for examining objects or patients using magnetic resonance tomography are known, for example, from DE10314215B4.
Modem magnetic resonance systems (MRT) operate with coils for transmitting high-frequency pulses for nuclear resonance excitation and/or for receiving induced magnetic resonance signals. A magnetic resonance system may include a permanent magnet or, more frequently, a superconducting coil for generating a substantially homogeneous basic magnetic field (H0) in an examination region, a large whole body coil (e.g., a body coil or BC) that may be integrated in a permanent manner in the MR device and a plurality of small local coils (e.g., surface coils or LC). To read out information, from which images of a patient may be generated, gradient coils for three axes (e.g., X and Y roughly radial to the patient and Z in the longitudinal direction of the patient) are used to read out selected regions of the object or patient to be examined. Local coding in magnetic resonance tomography may be implemented with the aid of a gradient coil arrangement with three independently activatable, magnetically orthogonal gradient field coil systems. By overlaying the three freely scalable fields (e.g., in three directions X, Y, Z), the orientation of the coding plane (‘gradient field’) may be selected freely.
Counter signals are transmitted between or in components of the MRT.
An EMC spectrum of a binary counter is determined by a dwell time of individual counter bits.
In the case of a counter with a clock rate of 10 MHz, bit[0] has a switching frequency of 5 MHz, bit[1] a switching frequency of 2.5 MHz, etc. The following applies: fBit=fcount/2N, where N is the bit position in the counter. Spectral frequencies result, as shown in FIG. 1.
In MR systems, spectral lines with frequencies that are not multiples of 2.5 MHz cause interference due to mixing effects. The prior art attempts to eliminate the problem by adequate shielding measures (e.g., housing, filter, shielded lines).